1. Technical Field
The present invention relates to a fixing device and an image forming apparatus incorporating the same, and more particularly, to a fixing device that fixes a toner image in place on a recording medium with heat and pressure, and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine incorporating several of those imaging functions, which employs such a fixing device.
2. Description of the Background Art
In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of those imaging functions, an image is formed by attracting developer or toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium by melting and setting the toner with heat and pressure.
Various types of fixing devices are known in the art, most of which employ a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip. As a recording medium bearing a toner image thereupon enters the fixing nip, the fuser member heats the recording medium to fuse and melt the toner particles, while the pressure member presses the recording medium against the fuser member to cause the molten toner to settle onto the recording medium.
One problem encountered when using such a fixing device is that a recording medium tends to curl or bend toward the fuser member, in a manner similar to that of a bimetallic strip, owing to expansion and contraction of its moisture content under heat through the fixing nip. Such curling causes the recording medium to eventually wind around the fuser member upon exiting the fixing nip, leading to malfunction or even failure of the fixing process.
To counteract the problem, there has been proposed a fixing device that includes a decurling member to prevent deformation of a recording medium passing downstream from a fixing nip along a media conveyance path.
According to this method, the decurling member comprises a protrusion disposed on a heater guide or frame that accommodates a heater having a flat, planar surface pressed against a pressure member through a fuser belt to establish a fixing nip therebetween. The protrusion is designed to contact the leading edge of a recording medium to direct it away from the fuser belt upon exiting the fixing nip, which allows the outgoing medium to proceed to a post-fixing unit along the media conveyance path without curling or deformation caused by the fixing process.